1. Technical Field
The present disclosure relates to a button detecting circuit, in particular, to a button detecting circuit which can detect a threshold voltage of a threshold unit disposed in a button module.
2. Description of Related Art
With the advancement of technology, a push-button input device has been widely used in electronic products. The push-button input device often has a button detecting circuit and a button network which is composed by a plurality of buttons. The button detecting circuit can generate a trigger signal based upon a button action of the button network. A back-end circuit determines which one of a plurality of buttons is pressed according to the trigger signal. In a typical push-button input device, one button is corresponding to one pin. When one of a plurality of buttons is pressed to turn on, the button detecting circuit generates the trigger signal correspondingly. Currently, some button detecting circuits are designed into multiple buttons sharing a single one pin to reduce chip area.
Please refer to FIG. 1, which shows a schematic diagram of a conventional button detecting circuit. The conventional button detecting circuit 1 includes a determining circuit 10, a voltage source 11 and a button module 14. The button module 14 works with a charging-discharging principle associate with a capacitor. Each button action of the button module 14 corresponds to an equivalent RC (Resistance-Capacitance) value, wherein the button action means at least one of a plurality of buttons is pressed. Each equivalent RC value corresponds to a different charging time. That is to say, the determining circuit 10 of the conventional button detecting circuit 1 determines which one of a plurality of buttons is pressed according to the charging time corresponding to different button actions.
Currently, one push-button input device often has a plurality of buttons, for example, the button module 14 shown in FIG. 1. The more buttons the push-button input device has, the higher precision the determining circuit 10 should have, such that the determining circuit 10 can exactly determine the button actions of the button module 14. However, cost of the determining circuit 10 also increases with a number of the buttons.
Hence, in order to solve the above problem of the cost of the determining circuit 10 increasing with the number of the buttons, a button detecting circuit is provided. The new button detecting circuit can determine the button actions of the button module, but also can solve the problem of the cost of the determining circuit increasing. On the other hand, the button module may comprise a light-emitting diode (LED) to instruct as to a state of the button module. Thus, suitable voltage should be provided to the button module. The LED will not be falsely triggered due to the voltage. The voltage will not affect the determining circuit to detect the button action of button module.